plasma and textiles by vignesh dhanabalan
TRANSCRIPT
WHAT IS PLASMA TECHNOLOGY?
The plasma is an ionized gas with equal density of positive and negative charges, which
exist over an extremely wide range of temperature and pressure. Examples of plasma
include the solar corona, a lightening bolt, a flame and a "neon" sign. The plasma consists
of free electrons, ions, radicals UV-radiation and other particles depending upon the gas
used.
PLASMA ON TEXTILES AND ITS USE
The plasma gas particles etch on the fabric surface in nano scale so as to modify the
functional properties of the fabric. Unlike conventional wet processes, which penetrate
deeply into fibers, plasma only reacts with the fabric surface that will not affect the
internal structure of the fibers. It can modify the surface properties of textile materials,
deposit chemical materials (plasma polymerization) to add up functionality, or remove
substances (plasma etching) from the textile materials
PLASMA TREATMENTS IN TEXTILE
TECHNOLOGY
Plasma treatment of textile fabrics and yarns is being investigated as an alternative to wet
chemical fabric treatment and pretreatment processes, e.g., shrink resistant or water
repellent finishing, which tent to alter fabric mechanical properties and are
environmentally hazardous. The transfer of research results into the technological field
would lead to non-polluting and very promising operating conditions. In the prospect of
chemical finishing using plasma, two main methods can be considered: grafting of a
compound on the fiber or surface modification by means of discharges. Plasma treatment
modifies the uppermost atomic layers of a material surface and leaves the bulk
characteristics unaffected. This treatment of textiles may result in desirable surface
modifications, including but not limited to surface etching, surface activation, cross
linking, chain scission, decrystallization, and oxidation. Treatment depends on the choice
of working gas and plasma density and energy. Air, oxygen, argon, fluorine, helium,
carbon dioxide or their mixtures can be used as plasma medium. The process result is
affected by the type of the gas used. Although the gas the same, if the fiber type is
different the result will be different (Textiles can be treated between two electrodes (in
fact in the plasma) or near the plasma region. Plasma-chemical conversion of the feed gas
produces chemically active particles that are able to modify textile surface molecules via
chemical reactions after impinging on the surface. The radicals generated inside the
plasma region must be given the opportunity to move to the reaction place at the textile
fiber surface. Thereby the path of radicals between the locations of generation and
reaction is limited on the one hand by the Distance between single fibers and on the other
hand by the gas density, i.e. by the mean distance between gas particles. Assuming
radicals react or recombine after several impacts with gas particles and at surface sites on
fibers there is a relationship between penetration depth of the plasma effect inside the
textile structure and process pressure as well as the textile structure itself .
A SCHEMATIC VIEW OF PLASMA DEVICE AND
DIFFERENT REACTIVE SPECIES
Plasma technology is used for innovative production techniques to improve the product
quality, as well as society requires new finishing techniques working in environmental
respect. Plasma surface treatments show distinct advantages, because they are able to
modify the surface properties of inert materials, sometimes with environment friendly
devices. For fabrics, cold plasma treatments require the development of reliable and large
Systems. Such systems now exist and the use of plasma physics in industrial problems is
rapidly increasing. On textile surfaces, three main effects can be obtained depending on
the treatment conditions: the cleaning effect, the increase of micro roughness (anti-pilling
finishing of wool) and the production of radicals to Obtain hydrophilic surfaces. Plasma
polymerisation, that is the deposition of solid polymeric materials with desired properties
on textile substrates, is under development. The advantage of such plasma treatments is
that the modification turns out to be restricted in the uppermost layers of the substrate,
thus not affecting the overall desirable bulk properties. . In terms of wet ability, polyester,
polypropylene, wool treated with plasma treatment often demonstrate better ability to
retain moisture or water droplets on their surface. Hydrophobic finishing, a treatment of
cotton fiber with identified plasma gas such as hexamethyldisiloxane (HMDSO), leads to
a smoother surface of cotton fabrics with increased contact angle of water. Plasma
technology also increases adhesion of chemical coating and enhances dye affinity of
textile materials. On the front of product quality, oxygen plasma gives anti-felting effect
on wool fiber without giving negative effects on hand feel and environment, as
conventional anti-felting approaches do. Different kinds of plasma gases provide
additional and special functionality to textile materials such as UV-protection, anti-
bacteria, medical, bleaching, and flame-retardant properties In medical engineering,
antibacterial and electrically conductive yarns are of great interest. Coating yarns with
silver makes them highly suitable for obtaining both properties. But the quantity of silver
applied as well as its adhesion to the yarns must be controlled in order to prevent it from
being washed out and from contaminating waste water. Therefore, plasma technology
also comes in here. High-energy particles are accelerated from the plasma onto a silver
plate, the target. In the process, silver atoms are ejected, which produces the coating on
the yarns. In this so-called sputter process, the coatings build up one atom layer at a time,
enabling control over the layers on a nano meter scale.
PLASMA SYNTHESIS PROCESSES.
Faraday proposed to classify the matter in four states: solid, liquid, gas and radiant.
Researches on the last form of matter started with the studies of Heinrich Geissler (1814-
1879): the new discovered phenomena, different from anything previously observed,
persuaded the scientists that they were facing with matter in a different state. Crookes
took again the term ”radiant matter” coined by Faraday to connect the radiant matter with
residual molecules of gas in a low-pressure tube. Sufficient additional energy, supplied to
gases by an electric field, creates plasma. For the treatment of fabrics, cold plasma is
used, where the ambient treatment atmosphere is near room temperature. It can be
produced in the glow discharge in a vacuum process or in more recent atmospheric
pressure plasma devices.
EFFECT OF PLASMA COATINGS ON THE
WATERPROOF CHARACTERISTICS OF FABRICS
Fabrics
Water
Column
(cm)
Contact
Angle (o)
Traditionally finished 32 133
Washed and plasma coated
(Fluorocarbon20%/Ar80%) 32 131
Washed and plasma coated
(Fluorocarbon90%/methane10%) 26 123
Washed and plasma coated
(Fluorocarbon93%/methane7%) 30 129
Plasma cleaned and plasma coated
(Fluorocarbon20%/Ar80%) 33 133
Plasma cleaned and plasma coated
Fluorocarbon90%/methane10%) 24 123
Plasma cleaned and plasma coated
(Fluorocarbon93%/methane7%) 37 140
Plasma cleaned and plasma coated
(Fluorocarbon90%/Ar10%) 34 134
Plasma cleaned and plasma grafted
(Unsaturated Fluorocarbon3%/Ar97%) 35 136
SHRINK RESISTANCE OF WOOL FIBERS
Plasma treatment has proved to be successful in the shrink-resist treatment of wool with a
simultaneously positive effect on the dyeing and printing. The morphology of wool is
highly complex, not only in the fibre stem but also on the surface as well. It is in fact the
surface morphology to play an important role in the wool processing. Unwanted effects
such as shrinkage, felting and barrier of diffusion are most probably due to the presence
of wool scales on the fibre surface. In the past, the modification of wool surface
morphology were conducted either by chemical degradation of scale (oxidative treatment
using chlorination) or by deposition of polymers on the scale . However, in both
processes, a large amount of chemicals generated from incomplete reactions polluted the
effluent. The oxidation is also required to reduce the hydrorepellance of wool to obtain
good dyability. Wool is composed at 95% of a natural polymer, the keratin. In the outer
part, the cuticle, the cells are in the form of scale .Cuticle cells overlap to create a
directional frictional coefficient: the scales are moved by water and they have the
tendency to close and join together with the typical movement that is proper to have a
good textile but it is also producing felting and shrinkage. Plasma treatment of wool has a
two-fold effect on the surface. First, the hydrophobic lipid layer on the surface is oxidised
and partially removed. Since the exocuticle, that is the layer of the surface itself
(epicuticle), is highly cross-linked via disulfide bridges, plasma treatment has a strong
effect on oxidising the disulfide bonds and reducing the cross-link density.
Table 1 Influence of the pretreatment on the area felting shrinkage of knitted Fabrics after 50 simulated washing cycles in a domestic washing machine
(TM 31).
Treatment Area felting shrinkage (%)
Untreated 69 Plasma-treated 21 Plasma/resin-treated 1.3 Chlorine/Hercosett-treated 1
A wool fiber in covered by cuticle scales. Very long cells are building the inner structure
of the fiber. The former plasma treatments on wool were done with the corona discharge
but it was not giving a uniform treatment on the fabric: the cuticle is modified, being
formed on the fiber micro roughness and holes. The corona discharge, consisting of a
series of small lightning-type discharges, has the advantage to be easily formed at
atmospheric pressure by applying a low frequency high voltage over an electrode pair.
Corona discharge is usually inhomogeneous and then problematic for textiles.
PLASMA TREATMENT FOR SYNTHETIC FIBERS
-performance fibers;
unfortu-nately, they are prone to hydrolysis. Thus, the application of a diffusion barrier to
the surface should reduce the tendency to hydrolyze in respective media. A
hexafluoroethane/hydrogen plasma is highly suitable to apply such a diffusion-barrier
layer to the surface. The resistance to 85 % H2SO4(20 h at room temperature) leaves the
fibers completely intact while conventional fluorocarbon finishing under the given
conditions produces significant shrinkage of the fibers in combination with loss of
properties
SEM pictures of Nomex-fibers after exposition in diluted H2SO4
HYDROPHOBIC FINISH ON COTTON
The mature cotton fibre is actually a dead, hollow cell wall composed almost entirely of
cellulose. The lengths of single cotton fibers vary, generally about one inch. It is
important to understand the relationship between the structure of this unique natural fibre
and its properties. The scanning electron micrograph can shows the extreme difference
between length and width of fiber and the flattened, twisted shapes formed when the fiber
dried. A variation in the structures of fiber cross sections is present. Since cotton fibers
are natural products and then quite different from each other some fibers contain more
Cellulose than others. Fibers with nearly full tubes have somewhat bean-shaped cross-
sections, but fibers with tubes that are not filled with cellulose are flatter.
The outer surface of the fiber, known as the cuticle, contains fats, waxes and pectins that
confer some adhesive properties to the fibbers, which together with natural twist of the
fiber means that cotton fibers are well suited to spin into yarns. When cotton yarns and
fabrics are desized, scoured and bleached, the cuticle is removed and it is possible to
obtain fibers with very high cellulose content. The textile surface has the property to be
less sensitive to spots After the plasma treatment, the researchers evaluated the surface
wet ability by means of the sessile drop technique, where a distilled water droplet is
placed on the fabric surface and observed through a telescope and the contact angle of the
droplet on the surface of the fabric was measured. If we observed a greater contact angle,
the greater is the surface hydrophobicity. Overall, the hydrophobicity of treated desized
denim fabrics was higher than that of treated sized denim fabrics. This indicates that sizes
on the denim fabrics play a role in determining surface wet ability even after fluorination
in a CF4, C3F6 plasma treatment
INDUSTRIAL DEVICES
Plasma are industrial useful because they possess at least one of two important
characteristics. The industrial applications are vaporizing bulk materials, welding, flame
spraying, and high temperature processing. The second major characteristic of plasma
relies upon the production of active species, that are more numerous, different in kind and
more energetic than those produced in chemical reaction. the so called Roll-to-Roll
textile treater and designed batch reactors according to client requests. CD Roll 1800 is a
Roll-to-Roll plasma treater used for the treatment of non woven and web material to
activate the surface prior to lamination, to improve wet ability and adhesion, and for a
hydrophobic/oleo phobic finishing with a plasma polymerisation. As active plasma
species they are using O2, N2, NH3 to increase wet ability and bonding ability to produce
sport wear fabrics.
the fabric is driven by a roll system, to pass among a set of rods that are electrodes
generating plasma. Rolls and rods are inserted into the vacuum chamber, and special
control devices must be used to monitor stresses in fabrics. Looking in the chamber,
during the plasma treatment, it is possible to see the glow discharge among electrode rods
APPLICATION OF PLASMA PARTICLES ON
FIBER
1) Enhance mechanical properties Softening of cotton and other cellulose-based
polymers, with a treatment by oxygen plasma. Reduced felting of wool with treatment by
oxygen plasma. Top resistance in wool, cotton, silk fabrics with the following treatment:
dipping in DMSO and subsequently N2-plasma.
.
2) Wetting Improvement of surface wetting in synthetic polymers (PA, PE, PP, PET
PTFE) with treatment in O2-, air-, NH3-plasma. Hydrophilic treatment serves also as
dirt-repellent and antistatic finish. Hydrophobic finishing of cotton, cotton/PET, with
treatment with siloxan- or per fluorocarbon- plasma. Oleo phobic finish for
cotton/polyester, by means of grafting of perfluoroacrylat.
3) Dyeing and printing. Improvement of capillarity in wool and cotton, with treatment
in oxygen plasma. Improved dyeing polyester with SiCl4-plasma and for polyamide with
Ar-plasma.
4) Composites and Laminates. Good adhesion between layers in laminates depends
upon the surface characteristics of fibers in layers and the interactions taking place at the
interface. A prerequisite condition of good adhesion remains the surface energy of fibers,
which can be modified with plasma treatments.
5) Applications in Membrane and Environmental Technology.
Gas separation to obtain oxygen enrichment.
Solution-Diffusion Membranes to obtain alcohol enrichment.
Ultra filtration membranes to improve selectivity.
Functionalized membranes such as affinity membranes, charged membranes,
bipolar membranes.
GRAFT COPOLYMERIZATION
Plasma grafting is grafting molecules on the material surface after plasma activation. The
effects of the plasma do not penetrate more than 100 from the surface. Because the bulk
of the material is not affected by the treatment, desirable structural characteristics are
maintained. Abidi & Hequet 2004 studied creating the active centers within the cellulose
chains which were used to initiate copolymerization reactions with vinyl monomers to
impart hydrophobic character to lightweight cotton fabric. N2, O2 and Ar plasmas were
obtained using a microwave generator at 2.45GHz under vacuum. To monitor the
changes UATR-FITR was used. Plasma treatment for 240 s with 500W was sufficient to
create active carbonyl groups. Ar plasma generated the most active groups. Before the
second plasma treatment, the fabrics were impregnated with vinyl laurite. According the
results for maximum grafting efficiency the vinyl monomer concentration should be
below 0,664 mol/l. Above this concentration, the homopolymerization reactions are
likely to be dominant. Testing of treated fabric revealed that excellent water repellency
was obtained (Abidi & Hequet, 2004)
RELATIVE FREE RADICAL INTENSITIES
DETECTED BY ESR AFTER THE PLASMA
TREATMENTS
Plasma gas Cotton Wool
O2 0.5 0.4
N2 0.6 0.5
Ar 1.6 0.6
H2 1.8 0.6
CO 2.9 0.7
Free radicals play an important role in polymerization, grafting, cross-linking and
implantation. Table 3 shows that free radical intensities are different for various gases
with the general rule that O2<N2<Ar<H2<CO<CF4 (Chen, 1996). The free radical
formation was increased with increasing time.
DISADVANTAGES
If the disadvantages of plasma treatments, such as the high cost of the plasma device, can
be eliminated, this technology will be valid and very important method for the textile
finishing industry.
CONCLUSION
Let us conclude telling the extra advantages of plasma treatments. The finished textile
shows better performance and improved colour fastness properties. Though currently not
very relevant in produced amounts, this type of high-performance textile will certainly
grow in economic importance. As a result of their high added value even small textile
batches can be produced at high profit, although perfect process control is absolutely
necessary. Typically, textiles for medical applications or uses in the sector of
biotechnology are expected to increase in importance. Key future applications such as
special selective filtrations, biocompatibility, and growing of biological tissues, would be
interesting fields for plasma physics